Compressing a T-1

By Joshua Erdman
Digital Foundation, inc.

I recently set up a client with a T-1 to connect their 2 offices. These offices were separated by 4 cities and distanced approximately 25 miles. The only data conection they could afford is a T-1 which naturally is not alot of bandwidth. Lucky for us, Cisco provides compression (only available for serial links, such as T-1, fractional T-1, and frame).

To compress a T-1 first connect to the remote router. Enter the global configuration and then the interface configuration, in my case it was:

conf t
int ser 0/0

now enable compression:

compress stac

Connect to your local router and perform the same steps.

After you have compression established, you want to analyze 2 things to make sure that this is helping and not hindering. One is CPU utilization. To check your CPU, use the command:

sho proc

Finally, you want to look at the compression ratios at a time when you expect peak bandwidth usage. I would say you want to shoot for a ratio of at least 1.2

Clue: It is not worth enabling compression if you get poor compression ratios or if the CPUs on your Cisco routers are too taxed. Some types of data when compressed actually grow in size. If the CPU utilization is too high, be prepared for increased latency and possible crashing.

Article last reviewed: 04/23/2004

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Created by: Digital Foundation, inc.

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